The invention relates to a device for converting the rotary motion of an eccentric driven by a motor shaft into a reciprocating motion of a working tool coupled with a shaft pin in electrically driven appliances, in whose housing a double-armed rocker arm provided with a shaft pin is pivotably mounted and an oscillating body is provided.
German AS No. 27 49 936 teaches an oscillating element for driving a cutter block of an electric dry shaver, comprising a drive plate for coupling to the cutter block, said plate comprising studs firmly attached to the housing and flexible in the direction of motion of the cutter block, and provided with a coupling arm flexible transversely to the direction of motion of the cutter block for coupling to the eccentric. This oscillating element is not only very costly to manufacture, but also suffers from the disadvantage that the oscillating motion of the drive plate produces a height loss which pulls the cutter block coupled to the drive arm, away from the cutting foil stretched around it.
Japanese Utility Model No. 57-57650 teaches a dry shaver with a rotary motor, an oscillating lower cutter, and a crank and rocker linkage to convert the rotary motion of the motor into an oscillating motion of the lower cutter. The motor shaft is aligned parallel to the lengthwise axis of the rocker arm engaging the lower cutter, and is disposed displaced laterally by the length of the crank rod. The crank rod is made fork-shaped in the vicinity of the rocker arm, whereby the rocker arm engages this fork and is held in a pivotable position in the fork by means of an articulation pin. The crank rod is also connected by an eccentric drive provided in the head of the connecting rod with the motor shaft of the rotary motor. An important disadvantage of this type of transmission is that the swing of the rocker arm is compensated by the rigid crank rod only with the accompaniment of considerable losses to pressure and friction in both bearing points, the articulation pin and eccentric drive, and the crank rod, whereby a large fraction of the power to be transmitted is lost and must necessarily be made up by applying additional energy. Increased energy consumption makes itself felt perceptibly disadvantageously to the user of such a device by virtue of the fact that after brief use, e.g. after a small number of shaves, the battery must be recharged or replaced.